Tire For Heavy Vehicles

ABSTRACT

A tire having a radial carcass reinforcement comprising a crown reinforcement formed of at least two working crown layers of inextensible reinforcement elements, which are crossed from one ply to the other, forming angles of between 10° and 45° with the circumferential direction, which itself is topped radially by a tread, said tread being joined to two beads by means of two sidewalls. The tire comprises additionally in each shoulder at least a layer of reinforcement elements which are parallel to each other in the layer and are oriented circumferentially, the axially inner end of said additional layer being radially adjacent to the edge of the radially outermost working crown layer, the axially outer end of said layer being located at a distance from the equatorial plane of the tire which is at least equal to the distance between said plane and the end of the working layer to which it is adjacent and the distance between said additional layer and the end of the axially widest working crown layer being greater than 1.5 mm.

The present invention relates to a tire having a radial carcassreinforcement, and more particularly to a tire intended to be fitted onvehicles bearing heavy loads and traveling at sustained speed, such as,for example, lorries, tractors, trailers or highway buses.

The reinforcement armature or reinforcement of tires and in particularof tires of vehicles of the heavy-vehicle type is currently—and mostfrequently—formed by stacking one or more plies conventionally referredto as “carcass plies”, “crown plies”, etc. This manner of designatingthe reinforcement armatures is derived from the manufacturing process,which consists of producing a series of semi-finished products in theform of plies, provided with cord reinforcing threads which arefrequently longitudinal, which plies are then assembled or stacked inorder to build a tire blank. The plies are produced flat, with largedimensions, and are subsequently cut according to the dimensions of agiven product. The plies are also assembled, in a first phase,substantially flat. The blank thus produced is then shaped to adopt thetoroidal profile typical of tires. The semi-finished products referredto as “finishing” products are then applied to the blank, to obtain aproduct ready to be vulcanized.

Such a “conventional” type of process involves, in particular for thephase of manufacture of the blank of the tire, the use of an anchoringelement (generally a bead wire), used for anchoring or holding thecarcass reinforcement in the zone of the beads of the tire. Thus, inthis type of process, a portion of all the plies constituting thecarcass reinforcement (or of only a part thereof) is turned up around abead wire arranged in the bead of the tire. In this manner, the carcassreinforcement is anchored in the bead.

The general adoption of this type of conventional process in theindustry, despite the numerous different ways of producing the plies andassemblies, has led the person skilled in the art to use a vocabularywhich reflects the process; hence the generally accepted terminology,comprising in particular the terms “plies”, “carcass”, “bead wire”,“shaping”, to designate the change from a flat profile to a toroidalprofile, etc.

There are nowadays tires which do not, properly speaking, comprise“plies” or “bead wires” in accordance with the preceding definitions.For example, document EP 0 582 196 describes tires manufactured withoutthe aid of semi-finished products in the form of plies. For example, thereinforcement elements of the different reinforcement structures areapplied directly to the adjacent layers of rubber mixes, the whole beingapplied in successive layers to a toroidal core the form of which makesit possible to obtain directly a profile similar to the final profile ofthe tire being manufactured. Thus, in this case, there are no longer any“semi-finished products”, nor “plies”, nor “bead wires”. The baseproducts, such as the rubber mixes and the reinforcement elements in theform of cords or filaments, are applied directly to the core. As thiscore is of toroidal form, the blank no longer needs to be shaped inorder to change from a flat profile to a profile in the form of a torus.

Furthermore, the tires described in this document do not have the“conventional” upturn of the carcass ply around a bead wire. This typeof anchoring is replaced by an arrangement in which circumferentialcords are arranged adjacent to said sidewall reinforcement structure,the whole being embedded in an anchoring or bonding rubber mix.

There are also processes for assembly on a toroidal core usingsemi-finished products specially adapted for quick, effective and simplelaying on a central core. Finally, it is also possible to use a mixturecomprising at the same time certain semi-finished products to producecertain architectural aspects (such as plies, bead wires, etc.), whereasothers are produced from the direct application of mixes and/orreinforcement elements.

In the present document, in order to take into account recenttechnological developments both in the field of manufacture and in thedesign of products, the conventional terms such as “plies”, “bead wires”etc. are advantageously replaced by neutral terms or terms which areindependent of the type of process used. Thus, the term “carcass-typereinforcing thread” or “sidewall reinforcing thread” is valid as adesignation for the reinforcement elements of a carcass ply in theconventional process, and the corresponding reinforcement elements,generally applied at the level of the sidewalls, of a tire producedusing a process without semi-finished products. The term “anchoringzone”, for its part, may equally well designate the “traditional” upturnof a carcass ply around a bead wire of a conventional process and theassembly formed by the circumferential reinforcement elements, therubber mix and the adjacent sidewall reinforcement portions of a bottomzone produced with a process using application on a toroidal core.

Generally in tires of the heavy-vehicle type, the carcass reinforcementis anchored on either side in the zone of the bead and is radiallysurmounted by a crown reinforcement formed of at least two layers whichare superposed and formed of cords or cables which are parallel in eachlayer. It may also comprise a layer of metal wires or cables of lowextensibility which form an angle of between 45° and 90° with thecircumferential direction, this ply, referred to as a triangulation ply,being radially located between the carcass reinforcement and the first,so-called working, crown ply, which are formed of parallel cords orcables having angles at most equal to 45° in absolute value. Thetriangulation ply forms with at least said working ply a triangulatedreinforcement, which undergoes little deformation under the differentstresses to which it is subjected, the essential role of thetriangulation ply being to absorb the transverse compressive forces towhich all the reinforcement elements in the zone of the crown of thetire are subject.

The crown reinforcement comprises at least one working layer; when saidcrown reinforcement comprises at least two working layers, these areformed of inextensible metallic reinforcement elements, which areparallel to each other within each layer and are crossed from one layerto the next, forming angles of between 10° and 45° with thecircumferential direction. Said working layers, which form the workingreinforcement, may also be covered by at least one so-called protectivelayer, formed of advantageously metallic, extensible reinforcementelements, which are referred to as “elastic elements”.

In the case of tires for “heavy vehicles”, a single protective layer isusually present and its protective elements, in the majority of cases,are oriented in the same direction and at the same angle in absolutevalue as those of the reinforcement elements of the working layer whichis radially outermost and therefore radially adjacent. In the case ofconstruction-vehicle tires which are intended to travel on relativelybumpy roads, it is advantageous for two protective layers to be present,the reinforcement elements being crossed from one layer to the next andthe reinforcement elements of the radially inner protective layer beingcrossed with the inextensible reinforcement elements of the radiallyouter working layer adjacent to said radially inner protective layer.

Cables are said to be inextensible when said cables have a relativeelongation at most equal to 0.2% under a tensile force equal to 10% ofthe breaking load.

Cables are said to be elastic when said cables have a relativeelongation at least equal to 4% under a tensile force equal to thebreaking load.

The circumferential direction of the tire, or longitudinal direction, isthe direction corresponding to the periphery of the tire and defined bythe direction of rolling of the tire.

The transverse or axial direction of the tire is parallel to the axis ofrotation of the tire.

The radial direction is a direction intersecting and perpendicular tothe axis of rotation of the tire.

The axis of rotation of the tire is the axis around which it rotates innormal use.

A radial or meridian plane is a plane containing the axis of rotation ofthe tire.

The circumferential median plane, or equatorial plane, is a plane whichis perpendicular to the axis of rotation of the tire and divides thetire into two halves.

Certain current tires, referred to as “highway” tires, are intended totravel at high speed and on increasingly long journeys, owing to theimprovement in road networks and the growth in motorway networksthroughout the world. All the conditions under which such a tire isrequired to travel without doubt make it possible to increase the numberof kilometers traveled, the wear of the tire being less; on the otherhand, the endurance of the latter, and in particular of the crownreinforcement, is impaired thereby.

There are in fact stresses at the level of the crown reinforcement andmore particularly shearing stresses between the crown layers, allied toa not insignificant increase in the operating temperature at the levelof the ends of the axially shortest crown layer, the consequence ofwhich is the appearance and propagation of cracks in the rubber at saidends.

In order to improve the endurance of the crown reinforcement of the typeof tire in question, solutions relating to the structure and quality ofthe layers and/or profiled elements of rubber mixes which are arrangedbetween and/or around the ends of plies, and more particularly the endsof the axially shortest ply, have already been provided.

French Patent 1 389 428, in order to improve the resistance todegradation of the rubber mixes located in the vicinity of the edges ofthe crown reinforcement, advocates the use, in combination with a treadof low hysteresis, of a rubber profiled element covering at least thesides and the marginal edges of the crown reinforcement and formed of arubber mix of low hysteresis.

French Patent FR 2 222 232, in order to avoid separations between crownreinforcement plies, teaches coating the ends of the reinforcement witha pad of rubber, the Shore A hardness of which differs from that of thetread surmounting said reinforcement, and is greater than the Shore Ahardness of the profiled element of rubber mix arranged between theedges of crown reinforcement plies and the carcass reinforcement.

French application FR 2 728 510 proposes arranging, firstly between thecarcass reinforcement and the crown reinforcement working ply radiallyclosest to the axis of rotation, an axially continuous ply, formed ofinextensible metal cables forming with the circumferential direction anangle at least equal to 60°, and the axial width of which is at leastequal to the axial width of the shortest working crown ply, and secondlybetween the two working crown plies an additional ply formed of metallicelements, which are oriented substantially parallel to thecircumferential direction.

Prolonged travel of the tires thus constructed caused fatigue failure toappear in the cables of the additional ply and more particularly theedges of said ply, whether the so-called triangulation ply is present ornot.

In order to overcome such drawbacks and improve the endurance of thecrown reinforcement of these tires, international application WO99/24269 proposes, on either side of the equatorial plane and in theimmediate axial extension of the additional ply of reinforcementelements which are substantially parallel to the circumferentialdirection, to couple, over a certain axial distance, the two workingcrown plies formed of reinforcement elements crossed from one ply to thenext, then to decouple them by means of profiled elements of rubber mixat least over the remainder of the width common to said two workingplies.

One aim of the invention is to provide tires for “heavy vehicles”, theendurance performance of which is improved still further compared withconventional tires.

This object is achieved according to the invention by a tire having aradial carcass reinforcement comprising a crown reinforcement formed ofat least two working crown layers of inextensible reinforcementelements, which are crossed from one ply to the other, forming angles ofbetween 10° and 45° with the circumferential direction, which itself istopped radially by a tread, said tread being joined to two beads bymeans of two sidewalls, said tire additionally comprising in eachshoulder at least one layer of reinforcement elements which are parallelto each other in the layer and are oriented circumferentially, theaxially inner end of said additional layer being radially adjacent tothe edge of the radially outermost working crown layer, the axiallyouter end of said additional layer being located at a distance from theequatorial plane of the tire which is at least equal to the distancebetween said plane and the end of the working layer to which it isadjacent and the distance between said additional layer and the end ofthe axially widest working crown layer being greater than 1.5 mm andpreferably between 2 and 12 mm.

According to one preferred embodiment of the invention, the axiallyouter end of said additional layer is axially external to the edge ofthe working crown layer to which it is adjacent.

According to a preferred variant embodiment of the invention, theaxially inner end of the additional layer is radially external to theedge of the radially outermost working crown layer and more preferablystill radially external and adjacent to the edge of the axially leastwide working crown layer. According to this latter variant of theinvention, the axially outer end of said additional layer is thenadvantageously axially external to the edge of the axially least wideworking crown layer.

Circumferential reinforcement elements are reinforcement elements whichform angles within the range +2.5°, −2.5° around 0° with thecircumferential direction.

The axial widths of the layers of reinforcement elements or axialpositions of the ends of said layers are measured on a cross-section ofa tire, the tire therefore being in a non-inflated state.

Tests carried out with tires thus defined according to the inventionhave shown that the performance in terms of endurance of the tire isimproved compared with tires of more traditional design which do notcomprise the additional layers such as described according to theinvention.

According to one preferred embodiment of the invention, a layer P ofcohesive rubber mixes is arranged between at least the ends of theworking crown layers, and the axially outer end of said layer P isaxially external to the end of the axially widest working crown layer.

The layer P thus defined on one hand results in decoupling of theworking crown layers which contributes per se to improving the enduranceof the tire and on the other hand will be able to contribute to ensuringa minimum distance greater than 1.5 mm between the additional layer ofcircumferential reinforcement elements and the end of the axially widestworking crown layer.

“Coupled plies” are to be understood to mean plies, the respectivereinforcement elements of which are separated radially by at most 1.5mm, said thickness of rubber being measured radially between the upperand lower generatrices respectively of said reinforcement elements.

According to one advantageous embodiment of the invention, the ratio ofthe elasticity modulus of the layer P to the elasticity modulus of thecalendering layer of the working layer adjacent to the additional layeris of between 0.5 and 1. The calendering layer in question is the layerof rubber which separates the reinforcement elements of the workinglayer from the layer P.

“Elasticity modulus” of a rubber mix is understood to mean a secantmodulus of extension at 10% deformation and at ambient temperature.

The measurements of modulus are carried out under tension in accordancewith Standard AFNOR-NFT-46002 of September 1988: the nominal secantmodulus (or apparent stress, in MPa) at 10% elongation is measured in asecond elongation (i.e. after an accommodation cycle) (normal conditionsof temperature and relative humidity in accordance with StandardAFNOR-NFT-40101 of December 1979).

According to this embodiment of the invention, the ratio of theelasticity moduli provided makes it possible in particular to obtaindecoupling of the working layers with lesser heat dissipation andtherefore lesser heating in this zone of the tire.

Preferably also, the axial width D of the layer P between the axiallyinner end of said layer P and the end of the axially least wide workingcrown ply is such that:

3·φ₂ ≦D≦20·φ₂

where φ₂ is the diameter of the reinforcement elements of the axiallyleast wide working crown ply. Such a relationship defines a zone ofengagement between the layer P of rubber mixes and the axially leastwide working ply. Such an engagement below a value equal to three timesthe diameter of the reinforcement elements of the radially outer workingply may not be sufficient to achieve decoupling of the working plies toobtain in particular attenuation of the stresses at the end of theaxially least wide working ply. A value of this engagement greater thantwenty times the diameter of the reinforcement elements of the axiallyleast wide working ply may result in an excessive reduction in the skidrigidity of the crown reinforcement of the tire.

Preferably, the axial width D of the layer of cohesive rubber mix Pbetween the axially inner end of said layer of cohesive rubber mix P andthe axially outer end of the axially least wide working crown layer isgreater than 5 mm.

The invention also preferably provides for the layer P, at the axiallyouter end of the axially least wide working crown ply, to have athickness such that the radial distance d between the two working crownplies, separated by said layer P, satisfies the relationship:

⅗·φ₂ <d<5·φ₂

where φ2 is the diameter of the reinforcement elements of the axiallyleast wide working crown ply.

The distance d is measured from cable to cable, that is to say betweenthe cable of a first working ply and the cable of a second working ply.In other words, this distance d covers the thickness of the layer P andthe respective thicknesses of the calendering rubber mixes, which areradially external to the cables of the radially inner working ply andradially internal to the cables of the radially outer working ply.

The different measurements of thickness are carried out on across-section of a tire, the tire therefore being in a non-inflatedstate.

According to one advantageous embodiment of the invention, at the end ofthe axially widest working crown layer, the thickness of the layer Pensures a distance d′, such that d′≧1.5 mm, between said end of theaxially widest working crown layer and the additional layer ofcircumferential reinforcement elements. The layer P of rubber mixesadvantageously also acts as a decoupling layer between the axiallywidest working layer and the additional layer of circumferentialreinforcement elements, such that the ends of the reinforcement elementsof the axially widest working layer are not stressed owing to theexcessive proximity of the circumferential reinforcement elements. Inother words, the circumferential reinforcement elements of theadditional layer advantageously do not penetrate a circle of radius d′centered on the end of the reinforcement elements of the axially widestworking layer.

As for the thickness d, the distance d′ is measured from cable to cableon a cross-section of a tire, the tire being in a non-inflated state.

According to one preferred embodiment of the invention, the axiallywidest working crown layer is radially to the inside of the otherworking crown layers.

Preferably also, the difference between the axial width of the axiallywidest working crown layer and the axial width of the axially least wideworking crown layer is between 5 and 30 mm.

According to one advantageous variant embodiment of the invention, theangle formed with the circumferential direction by the reinforcementelements of the working crown layers is less than 30° and preferablyless than 25°.

According to one variant embodiment of the invention, the working crownlayers comprise reinforcement elements, crossed from one ply to theother, forming angles with the circumferential direction which arevariable in the axial direction, said angles being greater on theaxially outer edges of the layers of reinforcement elements comparedwith the angles of said elements measured at the level of thecircumferential median plane. Such an embodiment of the invention makesit possible to increase the circumferential rigidity in some zones andon the contrary to reduce it in others, in particular in order to reducethe compressions of the carcass reinforcement.

One preferred embodiment of the invention also provides for the crownreinforcement to be finished off radially to the outside by at least onesupplementary layer, referred to as a protective layer, of what arecalled elastic reinforcement elements, which are oriented relative tothe circumferential direction at an angle of between 10° and 45° and ofthe same direction as the angle formed by the inextensible elements ofthe working layer which is radially adjacent thereto.

The protective layer may have an axial width less than the axial widthof the least wide working layer. Said protective layer may also have anaxial width greater than the axial width of the least wide workinglayer, such that it covers the edges of the least wide working layer.The protective layer formed of elastic reinforcement elements may, inthe latter case mentioned above, be on one hand possibly decoupled fromthe edges of said least wide working layer by profiled elements, andhave on the other hand an axial width less than or greater than theaxial width of the widest crown layer.

When the protective layer is axially narrower than the axially leastwide working crown layer, said working crown layer being radially theoutermost working layer, the invention advantageously provides for theedge of the protective layer to be radially adjacent and preferablyradially external to at least the axially inner edge of the additionallayer.

In comparison with the preceding variants of the invention, in order toobtain such an embodiment of the invention, in which the edge of theprotective layer is radially adjacent and external to the additionallayer, either the end of the protective layer is axially more to theoutside, or the axially inner end of the additional layer is axiallymore to the inside. In other words, either the protective layer isaxially wider, or the additional layer is axially wider, being extendedaxially towards the inside.

According to any one of the embodiments of the invention mentionedpreviously, the crown reinforcement may also be finished off, forexample radially between the carcass reinforcement and the radiallyinnermost working layer, by a triangulation layer formed of inextensiblereinforcement elements forming, with the circumferential direction, anangle greater than 40° and preferably of the same direction as that ofthe angle formed by the reinforcement elements of the layer radiallyclosest to the carcass reinforcement.

According to a first variant embodiment of the invention, thereinforcement elements of the additional layer of circumferentialreinforcement elements are metallic reinforcement elements.

According to another variant embodiment of the invention, thereinforcement elements of the additional layer of circumferentialreinforcement elements are textile reinforcement elements.

One advantageous embodiment of the invention provides for the crownreinforcement of the tire furthermore to comprise at least onecontinuous layer of circumferential reinforcement elements the axialwidth of which is preferably less than the axial width of the axiallywidest working crown layer.

The axial widths of the continuous layers of reinforcement elements aremeasured on a cross-section of a tire, the tire being in a non-inflatedstate.

The presence in the tire according to the invention of at least onecontinuous layer of circumferential reinforcement elements may make itpossible to contribute to obtaining virtually infinite radii of axialcurvature of the different reinforcement layers in a zone centered onthe circumferential median plane, which contributes to the enduranceperformance of the tire.

According to one advantageous embodiment of the invention, thereinforcement elements of at least one continuous layer ofcircumferential reinforcement elements are metallic reinforcementelements having a secant modulus at 0.7% elongation of between 10 and120 GPa and a maximum tangent modulus of less than 150 GPa.

According to a preferred embodiment, the secant modulus of thereinforcement elements at 0.7% elongation is less than 100 GPa andgreater than 20 GPa, preferably between 30 and 90 GPa and morepreferably still less than 80 GPa.

Preferably also, the maximum tangent modulus of the reinforcementelements is less than 130 GPa and more preferably still less than 120GPa.

The moduli expressed above are measured on a curve of tensile stress asa function of the elongation determined with a prestress of 20 MPareferred to the metal section of the reinforcement element, the tensilestress corresponding to a measured tension referred to the metal sectionof the reinforcement element.

The moduli of the same reinforcement elements may be measured on a curveof tensile stress as a function of the elongation determined with aprestress of 10 MPa referred to the overall section of the reinforcementelement, the tensile stress corresponding to a measured tension referredto the overall section of the reinforcement element. The overall sectionof the reinforcement element is the section of a composite elementformed of metal and of rubber, the latter having in particularpenetrated the reinforcement element during the phase of curing thetire.

According to this formulation relative to the overall section of thereinforcement element, the reinforcement elements of at least one layerof circumferential reinforcement elements are metallic reinforcementelements having a secant modulus at 0.7% elongation of between 5 and 60GPa and a maximum tangent modulus of less than 75 GPa.

According to a preferred embodiment, the secant modulus of thereinforcement elements at 0.7% elongation is less than 50 GPa andgreater than 10 GPa, preferably between 15 and 45 GPa and morepreferably still less than 40 GPa.

Preferably also, the maximum tangent modulus of the reinforcementelements is less than 65 GPa and more preferably still less than 60 GPa.

According to one preferred embodiment, the reinforcement elements of atleast one continuous layer of circumferential reinforcement elements aremetallic reinforcement elements having a curve of tensile stress as afunction of the relative elongation having shallow gradients for the lowelongations and a substantially constant, steep gradient for the higherelongations. Such reinforcement elements of the continuous layer ofcircumferential reinforcement elements are usually referred to as“bimodular” elements.

According to a preferred embodiment of the invention, the substantiallyconstant, steep gradient appears from a relative elongation of between0.1% and 0.5% onwards.

The different characteristics of the reinforcement elements mentionedabove are measured on reinforcement elements taken from tires.

Reinforcement elements which are more particularly suitable forproducing at least one continuous layer of circumferential reinforcementelements according to the invention are for example assemblies offormula 21.23, the construction of which is 3×(0.26+6×0.23) 4.4/6.6 SS;this stranded cable is formed of 21 elementary cords of formula 3×(1+6),with 3 strands twisted together each formed of 7 cords, one cord forminga central core of a diameter of 26/100 mm and 6 wound cords of adiameter of 23/100 mm. Such a cable has a secant modulus at 0.7% of 45GPa and a maximum tangent modulus of 98 GPa, both measured on a curve oftensile stress as a function of the elongation determined with aprestress of 20 MPa referred to the metal section of the reinforcementelement, the tensile stress corresponding to a measured tension referredto the metal section of the reinforcement element. On a curve of tensilestress as a function of the elongation determined with a prestress of 10MPa referred to the overall section of the reinforcement element, thetensile stress corresponding to a measured tension referred to theoverall section of the reinforcement element, this cable of formula21.23 has a secant modulus at 0.7% of 23 GPa and a maximum tangentmodulus of 49 GPa.

In the same manner, another example of reinforcement elements is anassembly of formula 21.28, the construction of which is 3×(0.32+6×0.28)6.2/9.3 SS. This cable has a secant modulus at 0.7% of 56 GPa and amaximum tangent modulus of 102 GPa, both measured on a curve of tensilestress as a function of the elongation determined with a prestress of 20MPa referred to the metal section of the reinforcement element, thetensile stress corresponding to a measured tension referred to the metalsection of the reinforcement element. On a curve of tensile stress as afunction of the elongation determined with a prestress of 10 MPareferred to the overall section of the reinforcement element, thetensile stress corresponding to a measured tension referred to theoverall section of the reinforcement element, this cable of formula21.28 has a secant modulus at 0.7% of 27 GPa and a maximum tangentmodulus of 49 GPa.

The use of such reinforcement elements in at least one continuous layerof circumferential reinforcement elements makes it possible inparticular to retain satisfactory rigidities of the layer includingafter the stages of shaping and of curing in conventional manufacturingprocesses.

According to a second embodiment of the invention, the circumferentialreinforcement elements of a continuous layer may be formed ofinextensible metallic elements cut so as to form sections of a lengthvery much less than the circumference of the least long layer, butpreferably greater than 0.1 times said circumference, the cuts betweensections being axially offset from each other. Preferably also, themodulus of elasticity in tension per unit of width of the continuouslayer of circumferential reinforcement elements is less than the modulusof elasticity in tension, measured under the same conditions, of themost extensible working crown layer. Such an embodiment makes itpossible to impart to the continuous layer of circumferentialreinforcement elements, in simple manner, a modulus which can easily beadjusted (by selecting the intervals between sections of one and thesame row), but which is in all cases lower than the modulus of the layerformed of the same metallic, but continuous, elements, the modulus ofthe continuous layer of circumferential reinforcement elements beingmeasured on a vulcanized layer of cut elements which is taken from thetire.

According to a third embodiment of the invention, the circumferentialreinforcement elements of a continuous layer are undulating metallicelements, the ratio a/λ of the amplitude of undulation to the wavelengthbeing at most equal to 0.09. Preferably, the modulus of elasticity intension per unit of width of the continuous layer of circumferentialreinforcement elements is less than the modulus of elasticity intension, measured under the same conditions, of the most extensibleworking crown layer.

The metallic elements are preferably steel cables.

According to one variant embodiment of the invention, at least onecontinuous layer of circumferential reinforcement elements is arrangedradially between two working crown layers.

According to the latter variant embodiment, the continuous layer ofcircumferential reinforcement elements makes it possible to limit moresignificantly the compression of the reinforcement elements of thecarcass reinforcement than a similar layer positioned radially to theoutside of the other working crown layers. It is preferably radiallyseparated from the carcass reinforcement by at least one working layerso as to limit the stresses on said reinforcement elements and not tofatigue them excessively.

Advantageously also in the case of a continuous layer of circumferentialreinforcement elements which is arranged radially between two workingcrown layers, the axial widths of the working crown layers radiallyadjacent to the layer of circumferential reinforcement elements aregreater than the axial width of said layer of circumferentialreinforcement elements.

Other advantageous details and characteristics of the invention willbecome apparent hereafter from the description of the examples ofembodiment of the invention with reference to FIGS. 1 to 5, whichdepict:

FIG. 1: a meridian view of a diagram of a tire according to oneembodiment of the invention,

FIG. 2: a meridian view of a diagram of a tire according to a secondembodiment of the invention,

FIG. 3: a meridian view of a diagram of a tire according to a thirdembodiment of the invention,

FIG. 4: a meridian view of a diagram of a tire according to a fourthembodiment of the invention,

FIG. 5: a meridian view of a diagram of a tire according to a fifthembodiment of the invention.

The figures are not shown to scale in order to simplify understandingthereof. The figures show only a half-view of a tire which is extendedsymmetrically relative to the axis XX′ which represents thecircumferential median plane, or equatorial plane, of a tire.

In FIG. 1, the tire 1, of dimension 295/60 R 22.5×, has a form ratio H/Sof 0.60, H being the height of the tire 1 on its mounting rim and S itsmaximum axial width. Said tire 1 comprises a radial carcassreinforcement 2 anchored in two beads, which are not shown in thefigure. The carcass reinforcement is formed of a single layer of metalcables. This carcass reinforcement 2 is wrapped by a crown reinforcement4, formed radially from the inside to the outside:

-   -   of a first working layer 41 formed of non-wrapped, inextensible        metal 11.35 cables which are continuous over the entire width of        the ply and oriented at an angle of 18°,    -   of a second working layer 42 formed of non-wrapped, inextensible        metal 11.35 cables which are continuous over the entire width of        the ply and oriented at an angle of 18° and crossed with the        metal cables of the layer 41; the layer 42 is axially smaller        than the layer 41,    -   of an additional layer 43 formed of circumferentially oriented        140/2 nylon cables; the layer 43 is radially external and        adjacent to the radially outer working layer 42 and extends        axially beyond the axially outer end of the layer 41.

The axial width L₄₁ of the first working layer 41 is equal to 234 mm.

The axial width L₄₂ of the second working layer 42 is equal to 216 mm.

The additional layer 43 of circumferential reinforcement elements has awidth of 42 mm; it has a zone of axial overlap with the layer 42 of 18mm.

The crown reinforcement is itself topped by a tread 5.

A rubber layer P, radially between and in contact with the working crownlayers 41 and 42, referred to as a decoupling rubber, covers the end ofsaid working layer 41 and extends beyond the axially outer end of saidlayer 41. The layer P of rubber mix provides in particular decouplingbetween the working layer 41 and the end of the radially outer workinglayer 42. The zone of engagement of the layer P between the two workinglayers 41 and 42 is defined by its thickness or more precisely theradial distance d between the end of the layer 42 and the layer 41 andby its axial width D between the axially inner end of said layer P andthe end of the radially outer working crown layer. The radial distance dis equal to 3.5 mm. The axial distance D is equal to 20 mm, orapproximately 13.3 times the diameter φ₂ of the reinforcement elementsof the working ply 42, the diameter φ₂ being equal to 1.5 mm.

The distance d′, as defined previously as being the distance between theend of the radially widest working crown layer 41 and the additionallayer 43, is for its part at least equal to 1.5 mm. The layer P thuscontributes according to the invention to maintaining a distance greaterthan 1.5 mm between the additional layer 43 and the end of the axiallywidest working crown layer 41.

The elasticity moduli of the layer P and of the calendering layer of thelayer 42 are identical and equal to 10 MPa; the ratio of said moduli istherefore equal to 1.

In FIG. 2, the tire 21 differs from the one shown in FIG. 1 firstly inthat the additional layer 243 of circumferential reinforcement elementshas a width of 18 mm and in that the distance between the axially outerend of said additional layer 243 and the axis XX′ is equal to thedistance between said plane and the end of the working layer 242. Thedistance d′, as defined previously as being the distance between the endof the radially widest working crown layer 241 and the additional layer243, is then at least equal to the distance d and therefore greater than3.5 mm.

Secondly, the tire 21 also differs from the one shown in FIG. 1 in thatit furthermore comprises:

-   -   a protective layer 244 formed of elastic metal 18×23 cables, the        axial width of which is equal to 160 mm.    -   a supplementary layer of reinforcement elements 245, referred to        as a triangulation layer, of a width substantially equal to 200        mm, formed of inextensible metal 9×28 cables. The reinforcement        elements of this layer 245 form an angle of approximately 45°        with the circumferential direction and are oriented in the same        direction as the reinforcement elements of the working layer        241. This layer 245 makes it possible in particular to        contribute to absorbing the transverse compressive stresses to        which all the reinforcement elements in the zone of the crown of        the tire are subject.

In FIG. 3, the tire 31 differs from the one shown in FIG. 1 in that itcomprises an additional layer 343 which is inserted between the twoworking layers 341, 342. The layer 343 is in fact radially adjacent andinternal to the layer 342. According to other embodiments according tothe invention which are not shown in the figures, the additional layer343 may also be radially adjacent to the layer 341 externally orinternally to said working layer 341.

FIG. 4 illustrates a variant embodiment of a tire 41 in accordance withthe invention which, compared with the embodiment of FIG. 2, furthermorecomprises a continuous layer 446 of circumferential reinforcementelements which is inserted between the working layers 441 and 442. Thiscontinuous layer 446 has a width L₄₄₆ of 196 mm, less than the widths ofthe working layers 441 and 442.

FIG. 5 illustrates yet another variant embodiment of a tire 51 accordingto the invention which, compared with the embodiment of FIG. 2, has aprotective layer 544 radially adjacent and external to the additionallayer 543. According to this embodiment, the axially inner end of theadditional layer 543 is thus radially between the working layer 542 andthe protective layer 544 over an axial width of 10 mm.

In FIG. 5, the protective layer has been widened relative to those ofthe other figures comprising such a protective layer; a similar resultnot shown in the figures may be obtained with a wider additional layer,the axially inner end of which is further to the inside in order toobtain an overlap with a protective layer which is axially narrower thanthat of FIG. 5.

Tests were carried out with the tire produced according to the inventionin accordance with the illustration of FIG. 2, and were compared with areference tire which is identical but produced using a conventionalconfiguration.

This conventional tire does not comprise the additional layers 43. Onthe other hand, it comprises protective and triangulation layers.

The first endurance tests were carried out by fitting identical vehicleswith each of the tires and making each of the vehicles followstraight-line paths, the tires being subjected to loads greater than therated load in order to speed up this type of test.

The reference vehicle comprising the conventional tires is associatedwith a load per tire of 3600 kg at the start of travel and changes toreach a load of 4350 kg at the end of travel.

The vehicle comprising the tires according to the invention isassociated with a load per tire of 3800 kg at the start of travel andchanges to reach a load of 4800 kg at the end of travel.

The tests are stopped when the tire is damaged and/or no longerfunctions normally.

The tests thus carried out showed that the vehicle fitted with tiresaccording to the invention covered a distance which is greater by 65%than the distance traveled by the reference vehicles. It would thereforeappear that the tires according to the invention are of distinctlyhigher performance than the reference tires even if they are subjectedto higher load stresses.

Other endurance tests were carried out on a test machine, alternatingsequences of turning to the left, turning to the right then traveling ina straight line under load conditions varying from 60 to 200% of therated load and thrust conditions varying from 0 to 0.35 times theapplied load. The speed is of between 30 and 70 km/h. The tests arestopped when the tire is damaged and/or no longer functions normally.

The results obtained show gains in terms of distances traveled by thetires according to the invention which are greater by 91% than thedistance traveled by the reference tires.

1. A tire having a radial carcass reinforcement comprising: a crownreinforcement formed of at least two working crown layers ofinextensible reinforcement elements, which are crossed from one ply tothe other, forming angles of between 10° and 45° with thecircumferential direction, which itself is topped radially by a tread,said tread being joined to two beads by means of two sidewalls; in eachshoulders at least one additional layer of reinforcement elements whichare parallel to each other in the layer and are orientedcircumferentially; wherein the axially inner end of said additionallayer is radially adjacent to the edge of the radially outermost workingcrown layer; wherein the axially outer end of said additional layer islocated at a distance from the equatorial plane of the tire which is atleast equal to the distance between said plane and the end of theworking layer to which it is adjacent; and wherein the distance betweensaid additional layer and the end of the axially widest working crownlayer is greater than 1.5 mm.
 2. The tire according to claim 1, whereinthe axially outer end of said additional layer is axially external tothe edge of the working crown layer to which it is adjacent.
 3. The tireaccording to claim 1 wherein the axially inner end of said additionallayer is radially external to the edge of the radially outermost workingcrown layer.
 4. The tire according to claim 3, at least two workinglayers having different axial widths, wherein the axially inner end ofsaid additional layer is radially external and adjacent to the edge ofthe axially least wide working crown layer.
 5. The tire according toclaim 1, wherein a layer P of cohesive rubber mixes is arranged betweenat least the ends of the working crown layers, and wherein the axiallyouter end of the layer P is axially external to the end of the axiallywidest working crown layer.
 6. The tire according to claim 5, whereinthe ratio of the elasticity modulus of the layer P to the elasticitymodulus of the calendering layer of the working layer adjacent to theadditional layer is of between 0.5 and
 1. 7. The tire according to claim5, wherein the axial width D of the layer P between the axially innerend of said layer P and the end of the axially least wide working crownply is such that:3·φ₂ ≦D≦20·φ₂ where φ₂ is the diameter of the reinforcement elements ofthe radially outer working crown ply.
 8. The tire according to claim 5,wherein the axial width D of the layer of cohesive rubber mix P betweenthe axially inner end of said layer of cohesive rubber mix P and theaxially outer end of the axially least wide working crown layer isgreater than 5 mm.
 9. The tire according to claim 5, wherein the layerP, at the axially outer end of the axially least wide working crown ply,has a thickness such that the radial distance d between the two workingcrown plies, separated by said layer P, satisfies the relationship:⅗·φ₂ <d<5·φ₂ where φ₂ is the diameter of the reinforcement elements ofthe radially outer working crown ply.
 10. The tire according to claim 5,wherein, at the end of the axially widest working crown layer, thethickness of the layer P ensures a distance d′, such that d′≧1.5 mm,between said end of the axially widest working crown layer and theadditional ply of circumferential reinforcement elements.
 11. The tireaccording to claim 1, wherein the axially widest working crown layer isradially to the inside of the other working crown layers.
 12. The tireaccording to claim 1, wherein the difference between the axial width ofthe axially widest working crown layer and the axial width of theaxially least wide working crown layer is between 5 and 30 mm.
 13. Thetire according to claim 1, wherein the angle formed with thecircumferential direction by the reinforcement elements of the workingcrown layers is less than 30° and preferably less than 25°.
 14. The tireaccording to claim 1, wherein the working crown layers comprisereinforcement elements, crossed from one ply to the other, formingangles with the circumferential direction which are variable in theaxial direction.
 15. The tire according to claim 1, wherein the crownreinforcement is finished off radially to the outside by at least onesupplementary ply, referred to as a protective ply, of what are calledelastic reinforcement elements, which are oriented relative to thecircumferential direction at an angle of between 10° and 45° and of thesame direction as the angle formed by the inextensible elements of theworking ply which is radially adjacent thereto.
 16. The tire accordingto claim 1, wherein the crown reinforcement comprises a triangulationlayer formed of metallic reinforcement elements forming angles with thecircumferential direction greater than 40°.
 17. The tire according toclaim 1, wherein the reinforcement elements of said additional layer ofcircumferential reinforcement elements are metallic reinforcementelements.
 18. The tire according to claim 1, wherein the reinforcementelements of said additional layer of circumferential reinforcementelements are textile reinforcement elements.
 19. The tire according toclaim 1, wherein the crown reinforcement comprises at least onecontinuous layer of circumferential reinforcement elements.
 20. The tireaccording to claim 19, wherein the axial width of at least onecontinuous layer of circumferential reinforcement elements is less thanthe axial width of the axially widest working crown layer.
 21. The tireaccording to claim 19, wherein at least one continuous layer ofcircumferential reinforcement elements is arranged radially between twoworking crown layers.
 22. The tire according to claim 21, wherein theaxial widths of the working crown layers radially adjacent to thecontinuous layer of circumferential reinforcement elements are greaterthan the axial width of said continuous layer of circumferentialreinforcement elements.
 23. The tire according to claim 19, wherein thereinforcement elements of at least one continuous layer ofcircumferential reinforcement elements are metallic reinforcementelements having a secant modulus at 0.7% elongation of between 10 and120 GPa and a maximum tangent modulus of less than 150 GPa.
 24. The tireaccording to claim 23, wherein the secant modulus of the reinforcementelements at 0.7% elongation is less than 100 GPa, preferably greaterthan 20 GPa and more preferably still of between 30 and 90 GPa.
 25. Thetire according to claim 23 wherein the maximum tangent modulus of thereinforcement elements is less than 130 GPa and preferably less than 120GPa.
 26. The tire according to claim 19, wherein the reinforcementelements of at least one continuous layer of circumferentialreinforcement elements are metallic reinforcement elements having acurve of tensile stress as a function of the relative elongation havingshallow gradients for the low elongations and a substantially constant,steep gradient for the higher elongations.
 27. The tire according toclaim 19, wherein the reinforcement elements of at least one continuouslayer of circumferential reinforcement elements are metallicreinforcement elements cut so as to form sections of a length less thanthe circumference of the least long ply, but greater than 0.1 times saidcircumference, the cuts between sections being axially offset from eachother, the modulus of elasticity in tension per unit of width of thecontinuous layer of circumferential reinforcement elements preferablybeing less than the modulus of elasticity in tension, measured under thesame conditions, of the most extensible working crown layer.
 28. Thetire according to claim 19, wherein the reinforcement elements of atleast one continuous layer of circumferential reinforcement elements areundulating metallic reinforcement elements, the ratio a/λ of theamplitude of undulation a to the wavelength λ being at most equal to0.09, the modulus of elasticity in tension per unit of width of thecontinuous layer of circumferential reinforcement elements preferablybeing less than the modulus of elasticity in tension, measured under thesame conditions, of the most extensible working crown layer.